Quantitative reconstruction of the refractive index in photosensitive materials via DIC phase imaging

Photosensitive materials are widely used in micro-/nanofabrication and photonic device development, where their refractive index (RI) distributions play a critical role in determining optical performances. To enable precise measurements of the RI distribution in photosensitive materials - particularly in the microstructures of photoresists - this study proposes a quantitative reconstruction method based on differential interference contrast (DIC) microscopy. Unlike conventional approaches requiring intermediate phase retrieval or interferometric systems, the proposed method directly reconstructs RI from intensity images acquired at multiple polarization angles and axial planes. A global optimization framework based on the first Born approximation enables high spatial resolution, rapid computation (∼30 s for images of 250 × 250 pixels), and high measurement accuracy. Experimental validation on periodic photoresist patterns shows a clear RI contrast between bleached and unbleached regions, with absolute relative errors of the RI reconstruction below 0.4% and mean absolute relative error of 0.17%. This technique offers a compact and efficient solution for quantitative RI characterization, with promising applicability in micro-/nanofabrication, photonic device inspection, and process monitoring.